Submarine bow diving planes may be designed to be capable of extending out of and retracting back into the hull of the submarine. Without such a capability, the bow diving planes could be damaged or cause damage to other ships or adjacent structures by inadvertent, uncontrolled movement of the submarine during rough weather. This is a particular concern when the submarine is moored alongside a pier or another ship, such as a tender. Further, it is desirable that the planesman be able to select whether the bow diving planes are in the extended or the retracted position as the submarine travels at sea.
The major assemblies involved in operating existing bow plane systems are the hydraulic tilt mechanism, the control surface shafting and bearings, and the interlock mechanism. The hydraulic tilt mechanism rotates the bow planes to the commanded angle when the planes are in the extended position. It consists of a hydraulic cylinder, located inside the pressure hull, and a mechanical linkage, which connects the hydraulic cylinder to the control surface shaft and bearing assembly located outside the pressure hull.
This existing bow diving plane design limits the bow planes in two respects. First, the bow planes must be fully extended before they can be rotated. Therefore, the only parameter which can be varied to control the hydrodynamic forces on the bow planes is the bow plane angle. Second, the port and starboard planes are constrained to rotate together because they are connected to a common shaft and ,operated by a single hydraulic tilting mechanism. Independent operation of the two bow planes would improve the stability of the submarine by counteracting its tendency to roll under certain operating conditions. Specifically, during a roll, independent bow planes could be set such that one bow plane has a rise angle and the other has a dive angle. This would apply a restoring moment to the submarine.
On existing submarines, the bow planes are more complex than the stern planes or the rudder in several respects. The interlock system and automatic greasing system are both unique to the bow planes. Also, the shaft and bearing assembly is more complex than that on any other control surfaces because it must transmit torque to the bow planes and telescope to extend and retract the planes. This complex system adds weight to the submarine and significantly increases the cost of purchase and maintenance of the submarine bow planes.
The automatic greasing system requires four hull penetrations for grease lines. The use of a hydraulic cylinder inside the pressure hull to operate the equipment outside the pressure hull results in the need for a hull penetration with a dynamic seal. The hull penetration is subject to submarine safety (SUBSAFE) requirements because the penetration affects the pressure integrity of the hull. In general, penetrations in the pressure hull are undesirable, but dynamic penetrations are even more so because they are difficult to maintain watertight. The dynamic seal makes the alignment between the piston rod and the operating rod critical to preventing binding at the hull penetration between the operating rod and the packing which seals around the rod. The interlock mechanism suffers from these same disadvantages because it also employs an inboard hydraulic cylinder to operate outboard equipment.